Battery In The Back

[Guest Battery Bill]

Hi all

Has anyone fitted their battery in the back of the car?

We were toying with the idea as it would not really lose any boot space if you fit it to one side. it would however gain a fair bit of space at the passanger footwell.

Can anyone see any obvious problems?

Cheers

[Guest 2BBoulton]

My only comment would be that in an event of an accident the battery may short and any spilled fuel may ignight

 

Bruce

[Guest TerryBarry]

The battery will be in a cooler environment back there.

The only disadvantage I can see is the few metres of hefty cable at £3.50 / m you will need to aquire.

Terry

[Guest Cantbearsed]

I used to drive Minis which have the battery in the wrong end and when the electrics went a bit "non-complient" (which was often in minis!!) I'd find the voltage at the battery to be about 1volt different to that at the front. As the battery cable is only 127" long maximum on a mini, I'd hate to think of the voltage drop you'd get from back to front on a RH ! Get the gauges out and give it a go....

[Guest 2BBoulton]

That reminds me, my Mini caught fire (twice) due to the positive cable wearing through due vibration and shorting out. I managed to save the car both times, the second time to the amusement of some passing coppers.

 

Lesson learned:- ensure that the gromets aren't worn out!

 

Bruce

[Guest Battery Bill]

Cantbearsed

I tried the setup using some Earth cable and going from the battery in the boot to the front , my multimeter did not record any voltage drop!

When you think of it its probably not any longer inside than a Mini anyhow.

 

Next question is could I use multi core earth cable the heavy duty stuff for (For house installations) as the supply (I have tons lying around) It is slightly wider than the Donor live supply wire and as it is multi core a degree of flexibility would be there. Not that it should be flexing much anyway with all the p clips in place.

[Guest TerryBarry]

The suitability of any cable you have is going to depend on the cross sectional area of the conductor.

Some single mains cables are to 6181Y specification - these are double insulated and therefore appear thicker.

Starter cable with cross- section of 25mm2 is rated to 170A compared with the 300A rating of 40mm2

The automotive cables will normally be more flexible than mains

25mm2 mains cable could be made up of 7 x 2.14mm dia conductors

the equivalent 25mm2 auto cable will be 37 x 0.9mm dia conductors.

HTH

Terry

[Guest daveg]

Bill

 

The length of un-fused cable scares me and the thinness of the insulation on earth cable scares me even more so I am going to put my battery up front

 

Dave

[Guest Battery Bill]

Terry

The Cable I have is 7 x 2.14 mm stuff!

Will that suffice or should I buy some automotive stuff?

I cant see the flexibility bit being an issue as it will be clipped up anyway.

[Guest Battery Bill]

Daveq

and the thinness of the insulation on earth cable scares me even more

OK we are getting somewhere now.

The insulation on the "earth cable" looks pretty similar to the Donors, I realise it is different type of plastic but surely the "House Earth cable" should be capable of taking higher voltages than a 12 v car system.

The length of un-fused cable scares me

, Whats wrong with putting an inline fuse in if it scares you that much?

Bill

[Guest daveg]

Bill

 

you cannot use a fuse 'cause the starter draws a HUGH current

 

The voltage isn't the issue wrt thickness of the insulation....its the fact that thats all you have between live and chassis

 

Dave

[Guest TerryBarry]

Bill,

If I were doing this I'd use automotive cable - 37 x 0.9mm or the heavier one as it's going to be a comparatively long length.

I'm not sure what current the starter motor draws - I've seen 160A quoted

The other thing to consider is the wiring to the fuse box.

I'm reusing the Sierra harness - this has four separate thinner feeds from the battery to fuse box. Two of these feeds have "fusible links" in them for protection. Would you extend these back to the battery or have some from of connection to the main positive lead up front to which these thinner leads connect.

Terry

[Guest Ant]

surely the "House Earth cable" should be capable of taking higher voltages than a 12 v car system

 

It's not _voltage_ that's the issue. It's high current is what burns out wires. They have a maximum rating and if you exceed that they get hot, melt the insulation, and short out. Household mains is essentially a low current setup. No main plug will handle more than 13 Amps, and the vast majority of household electrical items don't use more than 1 or 2 Amps. The entire lighting ring in modern houses is rated to 5 amps total, and 15 amps is the main ring on the sockets I think. Look in the fusebox on your Sierra and you'll find lots of 30 Amp fuses - main beam, headlights, wipers etc etc. Heated rear screens are 40 or more Amps aren't they?

 

This is because what you ultimately want is power.

 

Power = voltage x current.

 

Say you have a 60w bulb. At 240 volts the current is only 0.25 of an Amp (fractions in my head ... sheesh!). But at 12 volts you need 5 amps. This is 20 times more current because the voltage is 20 times less. The bulbs will be just as bright in both situations, but the wiring in the 12 volt system takes 20 times as much current.

 

So ... The easy answer is to look at the fuses for each circuit, and use wire of about 1 and a half times the fuse value. The mains cable, or any other cable, needs to be rated based on this value.

 

Flexibility is also an issue. Despite the P clips you get a lot of small vibrations in car cables. Vibrations on household wiring is virtually nill. Take a household wire and vibrate it repeatedly at a high frequency and eventually you will get metal flexing fatigue and its current carrying capabilities will drop - possibly over heating and melting the insulation.

 

The final point I've just thought of is temperatures. Household wiring is tpyically at 40 dec C or less. Behind the dash of a 2B gets significantly hotter than that because of the exhaust - even when wrapped etc. Is the insulation rated for those temperatures before any current is passed along the wire? Check the spec. It may be fine, but I'd want to be certain if I were you.

 

Ant

[Guest daveg]

Ant

 

So...all that can be summed up to "put the battery at the front for less hassel/risk"

 

Dave

PS That why they use 625,000 volts on the National Grid

[Guest Battery Bill]

Ant

The House earth cable I mean is the 7mm diameter stuff which is used before you get to the house!

OK Ok you are all picking on me I will buy some Automotive stuff, (Probably would have done so in the first place. :boohoo:

 

Terry

I'm reusing the Sierra harness - this has four separate thinner feeds from the battery to fuse box. Two of these feeds have "fusible links" in them for protection. Would you extend these back to the battery or have some from of connection to the main positive lead up front to which these thinner leads connect.

We are using a new 10 way fusebox and yes we had four seperate "Fusable linked thinner wires" (We now only have 3.

So I was thinking, one wire from the back up to a split to the fuses and Starter.

 

Daveq

So...all that can be summed up to "put the battery at the front for less hassel/risk"

We think its a good idea so there!

 

Well we will give it a go , thanks for your replies.

PS Is the battery not in the back of the Super spec?